I. Field
The present invention relates generally to communications, and more specifically to techniques for determining reverse link power control in an orthogonal communication system.
II. Background
In Frequency-Hopping Orthogonal Frequency Division Multiple Access (FH-OFDMA) system, bandwidth is evenly divided into a number of orthogonal sub-carriers. Each user is given a number of these OFDM sub-carriers. In FH-OFDMA, users will also be hopping (i.e., the subset of OFDM carriers assigned to each user changes over time) across the whole bandwidth. All users within the same sector or cell are orthogonal to each other and hence cause no interference to each other.
FH-OFDMA is an efficient multiplexing technique for high data rate transmission over wireless channels. However, due to a wide variation in the received Signal-to-Noise Ratio (SNR) in an FH-OFDMA system, it is highly resource-inefficient to ensure a small packet error rate on every transmission. A packet retransmission mechanism (e.g., H-ARQ) is often used to help avoid such inefficiency.
In addition, a closed-loop power control is often employed to ensure that sufficient SNR (i.e., SNR required to close the communication link) is received at the base station. There is an inherent tradeoff between number of (re)transmissions allowed and transmit power required for a successful transmission. For instance, by increasing the transmit power level; the number of transmissions required for a successful transmission can be decreased, which directly results in a higher data rate. Or, the transmit power required for a successful transmission can be decreased if the number of (re)transmissions allowed increases. This inherent tradeoff between rate and power adaptation makes the design of a power control loop for a system with retransmissions a nontrivial task.
There is therefore a need in the art for techniques that trade off rate and power in an effective manner taking into account retransmissions.